I think it's really good for a One-shot. In some stories, such as this one, it's not about development, it's about the tone and mood of the story, as well as the events. I've read this story at least ten times, and it never fails to make my heart ache. It's a sweet story. It's true there isn't much character development, there could be just a tiny bit more, but in such a story like this, I hardly think that's the main thing to focus on. It's a very good story, Yukiko Shi. I hope that you continue writing in the future!